This invention relates to methods and systems for estimating cylinder charge for internal combustion engines, and more particularly to methods and systems for estimating cylinder charge for internal combustion engines having variable valve timing (VVT).
As is known in the art, internal combustion engines with variable valve timing (VVT) are being introduced into the market place in an effort to improve fuel economy and emissions. As is also known in the art, engine controllers typically require an estimate of cylinder charge. Estimated cylinder charge is, however, significantly affected by valve timing. Furthermore, some such engines are equipped with cam profile switching (CPS), which depending on the various valve profiles, may also affect charge. The result is a significantly more complex charge estimation problem, as compared to conventional engine systems.
In accordance with the invention, a method is provided for determining at least one of cylinder air charge and cylinder burned gas for an internal combustion engine system. The engine system includes cylinders, each one of such cylinders having at least one intake valve and at least one exhaust valve in communication with such cylinder. The method determines one of a plurality of different scenarios, each one of the scenarios representing a geometrical relationship between opening and closing of the intake valve relative to closing of the exhaust valve. The at least one of the cylinder air charge and cylinder burned gas is calculated in accordance with the determined one of the plurality of scenarios.
In one embodiment, the engine system includes a memory for storing a plurality of different software modules. The method selects one of the plurality of software modules in accordance with the determined one of the plurality of scenarios. The at least one of the cylinder air charge and cylinder burned gas calculation comprises executing the selected one of the modules.
In one embodiment, a table, stored in a memory, such as a read only memory (ROM), provides a relationship between volume occupied by residual gas in the at least one cylinder at a predetermined position of the at least one cylinder in the engine during the cycle determined in accordance with each one of the plurality of scenarios for each of a plurality of different intake valve opening and exhaust valve closing conditions. The method includes: determining from the memory the volume occupied by residual gas in the at least one cylinder at a predetermined position of the at least one cylinder in the engine during the cycle for the intake valve opening and exhaust valve closing conditions; and, determining from the volume occupied by residual gas in the at least one cylinder at a predetermined position of the at least one cylinder in the engine during the cycle the at least one of the cylinder air charge and cylinder burned gas.
With such method, a geometric approach to charge estimation for throttled engines equipped with VVT, including the effects of CPS is provided.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.